1. Field of the Invention
The present invention generally relates to a method for testing large area integrated circuit chips and, more particularly, to utilizing a sacrificial metal level to create adequate size test pads and subsequently, after testing, removing the sacrificial metal level in a planarization step prior to the next metal level deposition.
2. Background Description
Manufacturing processes of large area integrated circuit (IC) chips tend to produce poor yields. This, in turn, increases the costs of the chips. It is therefore desirable to increase the yields of large area IC chips. Yields of large area IC chips could be improved by testing chip functionality prior to deposition of final metal levels. To achieve adequate test capability at such an intermediate level in the manufacturing process, sufficiently large pads must be available; however, such pads would normally interfere with subsequently deposited metal levels and vias.
It is therefore an object of the present invention to provide a way to test chip functionality at an intermediate level of the manufacturing process.
It is another object of the invention to provide sufficiently large test pads for testing chip functionality at an intermediate level of the manufacturing process in a way that does not interfere with subsequently deposited metal levels and vias.
It is yet another object of the invention to increase large area chip yields and increase throughput.
According to the invention, a process sequence is implemented in which a layer of insulator material is deposited over exposed vias in an intermediate metallization level, covering all the exposed vias. This insulator layer is then processed to selectively open areas over selected vias which are to be used for electrical testing. Those vias not selected for testing purposes remain covered with insulator layer. A sacrificial metal layer is deposited on the surface of the insulator layer. The deposited sacrificial metal layer is pattern etched to create adequately large test pad areas connected to exposed vias. After the testing is done, the sacrificial metal layer and the insulator layer are removed, preferably by a chemical-mechanical polish (CMP). Other techniques for removing the metal layer and the insulator layer may also be used, such as for example initially interposing a delaminating material or an etch stop between the insulator layer and the chip. After removal of the sacrificial metal layer and the insulator layer, normal subsequent backend of line (BEOL) processing is performed to complete the manufacturing process.
As an extension to this basic test process, test circuits can be formed around or beside the chip to be tested in the kerf areas separating the chip from other chips on the semiconductor wafer. Connections to the test circuits are in the sacrificial metal layer used to form the test pads. These connections to the test circuits are removed in the same way, e.g., by CMP. The test circuits, being located in the kerf areas, are simply scribed off after testing or in the process of sawing the wafer to separate the chips.